This invention relates to radar systems, and more particularly, to an improved radar system utilizing a method for compensating a received radar signal for both the pulse-to-pulse change in signal delay, and the pulse-to-pulse change in phase and frequency which occurs when an object producing a reflected signal is moving relative to the radar platform.
As is known in the art, coherent radar systems operate to detect a target by using the amplitude, frequency, and phase of a signal reflected by the object. In synthetic aperture radar systems (SAR), the platform on which the radar system is based may move an appreciable distance between the transmission of one radar pulse and the transmission of the next radar pulse. In addition, if the platform is based on a moving object (aircraft, ship or land-based vehicle), movement of the platform due to turbulence, wave motion, vehicle swaying, etc. creates another factor which must be taken into account to obtain accurate radar information. Further, it is typical in such radar systems to combine successive pulse returns for signal processing so to form a coherent array of pulse returns. There is thus both a time delay, a doppler frequency shift, and a phase shift between the various returns which must be taken into account for proper signal processing. Therefore, at least two forms of signal compensation should be implemented in a coherent radar system to insure a high degree of system accuracy; range closure compensation, and platform motion or doppler phase and frequency compensation.